At present, more and more electronic products, such as industrial control, medical treatment, communication and consumption etc., are intelligent with each passing day, and an embedded system with a microprocessor as its core gains increasingly extensive application. In many applications scenarios, the microprocessor needs to pick up some information or instructions of the surrounding environment, and by means of intelligent analyzing and processing, at last, outputs necessary control information. For example, the user uses various types of sensors for detecting or sensing outside signals, physical conditions (such as, light, heat, humidity) or chemical compositions (such as smog), etc., the sensor converts these information into electric signals with a definite format and transmits to the microprocessor to be analyzed and processed, and finally the microprocessor will perform the corresponding adjustment or control according to these information data.
Data acquisition cards are devices which acquire digital or analog signals from sensors or other equipments to be detected and send the signals to the microprocessor to be analyzed and processed. These data acquisition cards connect with a user circuit by a bus generally by using a general bus interface, wherein, the bus interface comprises types of ISA, PCI, PC/104, PXI, CPCI, USB, Fire Wire (1394) and Compact Flash, etc., and the bus usually divides into a parallel bus and a serial bus. For the parallel bus such as ISA, PCI, etc., the connected signal wires are so many that the signal transmission distance is short and the extensibility is insufficient; for the serial bus such as USB, 1394, etc., farther access distance is allowed and usage of the bus is convenient, but it has a higher requirement for the processor ability and the software system in the user circuit.
At present, some data acquisition cards having serial interfaces such as RS232, RS485, etc. appear on the market, and these data acquisition cards, after automatically acquiring input data signals, can send them to the user circuit by a communication protocol with a definite format, and receive the control of the output data signals of the user circuit. However, these data acquisition cards have the following drawbacks: firstly, some applications scenarios do not have the serial interfaces such as RS232/RS485, etc, and the software and physical condition are hard to support; secondly, the software communication and protocol bring about a certain impact to the usage of data acquisition card, not only there are problems of software upgrading and protocol compatibility and so on, but also the data acquisition card needs to complete data processing procedure such as decoding, verifying, etc., thus its extensibility and stability are both restricted by the data processing ability; for example, if the communication protocol is made to be very easy, then it needs a matched data verifying ability, and is inappropriate for using under the bad environment, and the extensibility is insufficient; and if the communication protocol is made to be very difficult, the user is hard to perform the accurate verification on it, then it is inconvenient to use.